The present invention relates to the measurement of the degradation in video sequences, and more particularly to a method of aligning two video sequences using selected partial pictures, one sequence being a reference sequence and the other being a processed sequence to be measured for degradation.
Conventional measurement of a video sequence has occurred in the analog, broadband domain using conventional waveform monitors and vectorscopes. As the video sequence moved into the digital domain, using a serial digital format, the resulting digital sequence has conventionally been converted into the analog, broadband domain for typical video measurements. However with the compression of the video sequence for storage or for transmission over lower bandwidth transmission media and subsequent decompression, the resulting decompressed video sequence is not an exact copy of the original, uncompressed video sequence. Other types of modifications to which the video sequence may be subjected include transmission through a CODEC, recording on tape, format conversion, satellite or broadcast transmission, composite encoding, etc. A measure of the amount of modification or degradation of the processed video sequence compared to a reference video sequence, the measure being related to the observability of flaws in the pictures by a human observer, is desired.
One such measurement instrument is disclosed in U.S. patent application Ser. No. 08/605,241 filed Feb. 12, 1996 by Bozidar Janko and David Fibush entitled "Programmable Instrument for Automatic Measurement of Compressed Video Quality" and is implemented in the PQA200 Picture Quality Analysis System manufactured by Tektronix, Inc. of Wilsonville, Oreg. The PQA200 compares a reference video sequence with a processed video sequence using a Just Noticeable Difference (JND) algorithm originally developed by David Sarnoff Research Laboratories, Inc. To assure that the pictures within the sequences to be compared are comparable and give consistent results from test to test, the comparable pictures are identified and aligned. The PQA200 uses identification and alignment markers that are added to the reference video sequence prior to processing and which are robust enough to survive the processing. By aligning the markers, consistent and meaningful measurements may be made. However these alignment markers, being within the active video portion of the pictures, are visible to an observer.
The American National Standards Institute (ANSI) standard T1.801.03-yyy, "Digital Transport of One-Way Video Signals--Parameters for Objective Performance Assessment", suggests using a correlation technique over the entire picture for each picture in the sequences being aligned. This is very compute intensive, with the resulting time required being such as to make realtime processes problematical.
What is desired is a method of video alignment between video sequences that is not visible to an observer and is capable of realtime processing.